The present invention relates to two piece fasteners and more particularly to fasteners having a design in which the strength to weight ratio has been optimized to provide a fastener having a preselected strength at an optimized weight and to a method for providing an optimized fastening system.
In the past, fasteners have been designed with significance being given to strength and cost. While weight has been a factor, the optimization of weight has not necessarily been of prime consideration. With the advent of emphasis on fuel efficiency and on the attendant considerations of cost and availability of lightweight materials, economy in weight and efficiency in material utilization has become more significant in fastener design. This is especially true in the aerospace industry.
The present invention is specifically described for applications of two piece swage type fasteners of the type illustrated in U.S. Pat. Nos. 3,915,053 to J. Ruhl, issued Oct. 28, 1975 and U.S. Pat. No. 2,531,048 to L. Huck, issued Nov. 21, 1950. Thus the present invention will be described in connection with a two piece fastener comprised of a pin and a collar adapted to be swaged into lockgrooves in the pin. It should be understood, however, that certain features of the present invention may apply to nonswaged type fasteners.
Features of the present invention can be generally considered to include, but are not limited to, the following:
1. Reduction in overall fastener size by preselection of the ultimate shear stress of the materials of the pin member and collar to have an ultimate shear stress ratio within a preselected range, PA0 2. Providing improved fill or packing between the swaged collar and the lockgrooves of the pin, PA0 3. Reducing the size of the collar for a preselected tensile load carrying capacity of the fastener whereby ultimate failure can incipiently occur in shear and/or compressive failure of the collar, PA0 4. For a pull type, swage fastener having a pin with a breakneck groove, providing the breakneck groove with a preselected stress concentration factor whereby the fastener can be set or installed on a surface having an angulation up to at least 7.degree..
Therefore, it is a general object of the present invention to provide an improved, optimized lightweight fastening system.
It is another general object of the present invention to provide an improved fastening system including one or more of the features noted above and those as shown and described.